The mysterious disappearance of a small island off the coast of Yucatan more than a decade ago is being linked to a 2000 agreement negotiated between the US and Mexico that redefined the territorial limits in the Gulf of Mexico. The pact negotiated by former Presidents Ernesto Zedillo and Bill Clinton established boundaries in previously undefined areas in order to determine drilling rights for crude oil. Some Mexican legislators contend that the Mexican government ceded a large part of its territorial rights to the US during the negotiations. A key to determine Mexico's boundary was the tiny Isla Bermeja, which had been 160 km off the coast of Yucatan and Campeche states but was no longer visible when the negotiations were concluded in 2000. Island was key to territorial accord with US Six senators from the governing Partido Accion Nacional (PAN) raised the question about Isla Bermeja on the floor of the Senate in early November, citing "plentiful suspicions" that the island may have been caused to vanish on purpose. The senators said the island disappeared "mysteriously" some time before the Zedillo and Clinton governments began negotiations on an agreement on the disputed area. Under the agreement, the US and Mexican governments divided a zone spanning 17,790 sq km in the Gulf of Mexico known as the Donut Hole.